1. Field of the Invention
The present invention relates to a multiple power source system that includes both a high tension electric system driven by high tension electric energy and a low tension electric system driven by lower tension electric energy. More specifically the invention pertains to a multiple power source system that compensates for an insufficiency of electric energy in a certain electric system, as well as to an apparatus and a vehicle with the multiple power source system mounted thereon.
2. Description of the Related Art
Electric energy is usable in a wide range of technical fields including thermal, optical, power-driven, and data communication, and is used as the energy power source of various industries. Each apparatus utilizing the electric energy has predetermined ratings and ensures the normal operations under predetermined rated voltage and power. A typical industrial apparatus includes a plurality of devices having different rated voltages and a plurality of power sources having different line voltages for these devices. By way of example, an electric vehicle has a high voltage motor used for driving the vehicle and a low tension electric system used for, for example, a computer, which controls the output torque of the motor, lamps, controllers, and auxiliary machines.
With the advance of semiconductor technology, the use of semiconductor elements, such as power transistors and thyristors, desirably simplifies the structure of a power converter unit like an inverter, a converter, or a chopper circuit. These power converters are controlled with a high accuracy by the computer. The recently developed industrial apparatus includes a charge-discharge unit that enables charge and discharge of electric energy, for example, a battery or a power capacitor, as at least one of the plural power sources. For the purpose of energy saving, non-required mechanical energy is regenerated as electric energy and charged into the charge-discharge unit. An auxiliary power source is provided as a back-up power source in the case of a failure of the main power source.
In the apparatus having the plurality of power sources, contacts and diodes are generally required to connect the plurality of power sources with the devices. This makes the structure of the apparatus rather complicated. For example, a device with a contact, such as a relay, is required to selectively connect a power source of interest with an actuator. A diode having the rectifying function may be used to prevent the electric current from flowing from the high voltage power source to the low voltage power source. The structure of switching the relay or another contact may be replaced with a structure having duplicate motor windings, where each coil is independently connected to the power source. These structures, however, make the apparatus undesirably bulky.
The apparatus having the plurality of power sources may not work properly when either one of the high voltage power source and the low voltage power source has an insufficiency of electric power. In order to solve this problem, a voltage step-up and step-down circuit is provided to enable the electric energy to be supplied to the electric system having an insufficiency of electric energy. This structure enables one electric system having sufficient electric energy to give the excess electric energy to another electric system having insufficient electric energy This effectively reduces the possible malfunction of the industrial apparatus.
In this case, however, a separate circuit is required to step up and down the voltage between the plurality of power sources. This undesirably increases the required number of electric parts and makes the power source circuit rather complicated, thereby increasing the manufacturing cost and lowering the reliability. The voltage step-up and step-down circuit uses a reactor for converting the electric energy to magnetic energy and reconverting the magnetic energy to electric energy. A large reactor is required to accumulate a sufficiently large magnetic energy. Even the step-up and step-down circuit, which is provided only for the emergency purpose to compensate for the insufficient electric power in a power source system, thus occupies a relatively large space and increases the total weight of the industrial apparatus.
The object of the present invention is thus to simplify the structure of a multiple power source system having a plurality of power sources for driving a three-phase motor, and also to simplify the structure of an apparatus, for example, a hybrid vehicle, with the multiple power source system mounted thereon.
At least part of the above and the other related objects is attained by a multiple power source system that supplies an electric power to a three-phase motor, which has Y-connected windings. The multiple power source system includes: a first direct current power source; a power control circuit that is disposed between the first direct current power source and the Y-connected windings of the three-phase motor and has switching elements, which are switched on and off to supply an electric power output from the first direct current power source to the three-phase motor; and a second direct current power source that is different from the first direct current power source. In the multiple power source system, one terminal of the second direct current power source is connected with a terminal of the first direct current power source having an identical polarity. The other terminal of the second direct current power source is connected with a neutral point of the Y-connected windings in the three-phase motor.
The multiple power source system of the present invention enables the two direct current power sources to be connected with each other by a simple arrangement of connection without using any contacts or diodes.
The multiple power source system of the present invention has a variety of possible applications. In accordance with one possible application, the first direct current power source is chargeable with a higher voltage than the second direct current power source. The multiple power source system of this application further includes a charge unit that controls switch-on and -off operations of a specific switching element, which is connected to a specific winding selected among the Y-connected windings of the three-phase motor, so as to step up a voltage using the specific winding, thereby causing the first direct current power source to be charged with an electric power output from the second direct current power source. This arrangement significantly simplifies the structure of charging the first direct current power source with the second direct current power source. This accordingly reduces the size and the manufacturing cost of the whole system and improves the reliability. This structure does not require any semiconductor elements or reactors (windings) for the voltage step-up circuit.
In the multiple power source system of the present invention, the windings of the three-phase motor and the switching elements of the power control circuit are utilized as the constituents of the voltage step-up circuit of the charge unit. This ensures the effective use of the electric parts.
In accordance with one preferable embodiment of the present invention, the power control circuit includes a pair of the switching elements that are provided for each of the windings of the three-phase motor and are interposed between a positive power line and a negative power line of the first direct current power source. Each of the switching elements is connected with a protection diode. A connection point of each pair of the switching elements is connected to the corresponding winding. The charge unit switches on a switching element that is selected among the pairs of the switching elements and is included in a closed circuit including the second direct current power source and the corresponding winding, and subsequently turns off the selected switching element, so as to cause the first direct current power source to be charged via the protection diode. This arrangement simplifies the structure of the voltage step-up circuit.
In one preferable structure of the above application, the multiple power source system has a charge sensor that measures a charge level of the first direct current power source by the charge unit, and a charge control circuit that controls a working condition of the charge unit, based on the observed charge level by the charge sensor. This circuit structure enables the electrical energy to be automatically supplemented for the direct current power source having an insufficient level of the remaining charge.
In accordance with one embodiment of this structure, the charge control circuit includes a detection unit that detects a charging state of the first direct current power source, based on the observed charge level by the charge sensor; and a working condition determination unit that determines the working condition of the charge unit, based on a result of the detection by the detection unit. This structure enables the charging operation of the charge unit to be automatically concluded. The charge sensor may directly measure the charge and/or discharge electric current of the charge unit, so as to determine the charge level of the first direct current power source by the charge unit. The charge sensor may alternatively estimate the charge level indirectly from a working condition of an apparatus that is driven with the charge unit as the power source. It is preferable that the working condition determination unit, which determines the working condition of the charge unit, not only controls a start and a termination of the charging operation of the charge unit, but regulates the step-up voltage or the step-down voltage of the charge unit, in order to prevent an excessive load from being applied to the charge unit. For example, when the charge unit is a voltage step-up and step-down chopper circuit, the working condition determination unit regulates the duty ratio of a semiconductor switching element included in the chopper circuit, thereby readily regulating the step-up voltage or the step-down voltage of the charge unit.
In accordance with another preferable application of the present invention, the multiple power source system further includes: a connection switching unit that switches a connection of a circuit including the second direct current power source and the neutral point of the Y-connected windings between a substantially closed state and an open state; and a connection control unit that, when the charge unit starts working, drives the connection switching unit to set the connection of the circuit including the second direct current power source and the neutral point of the Y-connected windings in the substantially closed state.
It is preferable that one of the plural direct current power sources used for a control circuit, such as a computer, is grounded or electromagnetically shielded for the noise reduction. In some cases, it may be preferable that the other power source is kept in a floating state. Only when a supplement of electric energy is required, these plural direct current power sources are connected with each other. Otherwise the power sources are substantially kept in the insulating state (including the state of the high impedance).
It is preferable that the first direct current power source is either a battery or a high-power capacitor. The battery may be any one of known secondary batteries that utilize electrochemical reactions to accumulate the electric energy, for example, lead acid batteries, nickel hydrogen batteries, nickel cadmium batteries, lithium ion batteries, and lithium polymer batteries. The secondary battery enables the storage of electric power for a relatively longer time period than a conventional capacitor. An example of the high-power capacitor is an double electric layer capacitor. The capacitor has the self discharge property and is generally required charging in use. The electric system utilizing a power capacitor accordingly requires a charging circuit to charge the power capacitor. The structure of the multiple power source system of the present invention may be utilized as this charging circuit. In the system that has a separate charging circuit for the high-power capacitor, the structure of the multiple power source system of the present invention may be used in the case of malfunction of the separate charging circuit or in the case of an insufficiency of the electric energy.
In the circuit structure that performs charging, the three-phase motor may have xcex94-connected windings, in place of the Y-connected windings. In this case, the other terminal of the second direct current power source is connected to one terminal of the xcex94-connected windings, in place of the neutral point of the Y-connected windings. The first direct current power source is chargeable with a higher voltage than the second direct current power source. The multiple power source system of this application further includes a charge unit that controls switch-on and -off operations of a specific switching element that is connected to a specific winding, to which the other terminal of the second direct current power source is not directly connected, in order to step up a voltage using the specific winding of the three-phase motor, thereby causing the first direct current power source to be charged with an electric power output from the second direct current power source. In the case of the xcex94-connection, one of the windings can not be used for the voltage step-up, but otherwise the xcex94-connection ensures a similar voltage step-up circuit to that of the Y-connection.
In the circuit structure that utilizes the windings of the three-phase motor, the Y-connection enables any of the windings to be used for the voltage step-up and charging. In the case of the three-phase motor, there are three charging circuits that respectively utilize the three windings. In the case of the xcex94-connection, the windings, to which the other terminal of the second direct current power source is not directly connected, may be used for the voltage step-up. There are thus still duplicate charging circuits. The multiple charging circuits enable the voltage step-up and charging process, which requires a certain time period, to be carried out by utilizing the plurality of windings, thereby shortening the required charging time. This structure also enables the three-phase magnetic circuits utilizing the respective windings to be used equally.
The multiple power source system of the present invention may be incorporated in a variety of apparatuses, and is effectively used, for example, in a structure that has a starting motor, which is driven only at the time of staring to start an engine, in one of the power systems. In a typical structure of the apparatus having an engine that is driven directly with a fuel, once the engine starts, a generator is driven to supply the required electric power. In this structure, it is required to supply the electric power for driving the starting motor only at the time of starting the engine. The charge unit is driven to accumulate the electric energy required for the starting operation in the battery or in the high-power capacitor, and the engine is started with the accumulated electric energy. The charging time is practically shortened when the charge unit is driven to accumulate only the electric energy required for the starting operation in the battery or in the high-power capacitor. Examples of the apparatus having this structure include a hybrid vehicle with both an internal combustion engine and a motor mounted thereon to drive the vehicle, and a vehicle with a motor for a compressor, which is a power source of an air conditioner mounted on the vehicle and requires a large electric energy only at a starting time.
The present invention is also directed to a motor driving apparatus that utilizes the multiple power source system. In the multiple power source system, the three-phase motor can be unipolar driven by means of a closed circuit including the second direct current power source, a selected switching element, and the corresponding winding. The motor driving apparatus may include: a first motor drive unit that causes the power control circuit to drive the three-phase motor by means of the first direct current power source; and a second motor drive unit that independently switches on and off the switching elements that are connected to power lines of the connection of the first direct current power source with the second direct current power source, and unipolar driving the three-phase motor by means of the second direct current power source. In this application, the second motor drive unit uses the second direct current power source to make the electric current flow through each winding of the three-phase motor. This enables the three-phase motor to be unipolar driven.
In accordance with one preferable embodiment of the motor driving apparatus, the power control circuit includes a pair of the switching elements that are provided for each of the windings of the three-phase motor and are interposed between a positive power line and a negative power line of the first direct current power source. A connection point of each pair of the switching elements is connected to the corresponding winding. The second motor drive unit successively switches on and off one of each pair of the switched elements to form a closed circuit including the second direct current power source and the corresponding winding, thereby generating a field in the three-phase motor.
In the motor driving apparatus, the three-phase motor may have xcex94-connected windings, in place of the Y-connected windings. In this case, the other terminal of the second direct current power source is connected to one terminal of the xcex94-connected windings, in place of the neutral point of the Y-connected windings. The motor driving apparatus includes: a first motor drive unit that causes the power control circuit to drive the three-phase motor by means of the first direct current power source; and a second motor drive unit that independently switches on and off switching elements, to which the other terminal of the second direct current power source is not directly connected, among the switching elements that are connected to power lines of the connection of the first direct current power source with the second direct current power source, and irregular unipolar driving the three-phase motor by means of the second direct current power source. In this structure, all the windings of the three-phase motor can not be used, but two phase windings can be used to drive the three-phase motor.
The motor driving apparatus of the present invention may be applied to a vehicle with an engine, which is directly driven with a fuel, mounted thereon as one of the drive sources. In such a vehicle, the three-phase motor is connected with either one of a drive shaft of the vehicle and a rotating shaft of the engine. The drive shaft is driven according to a driving state of the vehicle with at least one of a power output from the engine and a power output from the three-phase motor.
The multiple power source system of the present invention is not restricted to the applications discussed above, but there may be a variety of other applications. There may be a plurality of three-phase motors having windings and a plurality of charge units. In the multiple power source system of the present invention, multiple charging circuits laid out in a multi-layer configuration may be constructed by utilizing the windings of the plural three-phase motors and the plural charge units. In the case of m-layer, n-multiple charging circuits, the accumulated charge is carried out with n output electric currents having the phases shifted by 2xcfx80/n at an identical on-time ratio having the electrical angle shifted by 2xcfx80/m.
The multiple power source system may additionally include known electric elements. For example, when the direct current power source has a significantly large inductance, a low-pass filter may be added to prevent the switching properties of the switching elements from being worsened by the large inductance. The reactance, the capacitor, and the resistor used as the parts of other electric circuits may be used for the electric elements included in the low-pass filter.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.